The present invention relates generally to aircraft weapons systems, and more particularly to store carriers for carrying a releasable store on an aircraft.
Military aircraft utilize racks located beneath the wings and fuselage to carry and dispense stores upon command. Stores may be used to contain munitions i.e. bombs, or to contain other material to be dropped from the aircraft i.e. rockets or missiles upon command. Typical ejector racks are shown in U.S. Pat. Nos. 4,043,525 and 4,347,777, which are herein incorporated by reference.
Conventionally, an ejector rack includes a release mechanism which is activated to mechanically release and subsequently forcibly eject the stores from the aircraft. Most ejector racks at one time utilized pyrotechnic (explosive) cartridges which, upon ignition, generate high pressure gas for actuating the mechanical release mechanism, as well as providing high pressure gas to forcibly eject the store from the rack mounted on the aircraft.
Ejection systems that employ pyrotechnic cartridges have certain undesirable characteristics. For example, a great deal of cleaning and maintenance is required after firing a pyrotechnic cartridge. When fired, the chemical burning of the explosive charge within the pyrotechnic cartridge results in a large amount of residue being deposited within the system. This residue also contains moisture and corrosives. After burning, the moisture in the system tends to further gather debris, form ice, and otherwise clog the internal and external workings of the bomb rack mechanism. If not properly disassembled and cleaned after a scheduled number of firings, at high cost and a great deal of labor and downtime for the aircraft, an ejection system utilizing pyrotechnic cartridges will quickly corrode and become unreliable.
In order to avoid the inherent problems associated with the pyrotechnic cartridge, the inventor of the present invention devised a unique pneumatic ejector rack assembly set forth in U.S. Pat. No. 5,583,312 (hereinafter referred to as the ""312 patent) entitled COLD GAS EJECTOR RACK, issued Dec. 10, 1996, which is herein incorporated by reference. The ""312 patent describes a pressurization system capable of servicing one or more store release systems, which system uses air or one of any number of clean, non-pyrotechnic pressurized gases both as the energy source and energy transfer medium. Preferably, the aircraft contains a miniature compressor and purification system. Ambient air is filtered, dried and stored as an energy medium. Using purified air eliminates the excessive cleaning burden imposed when using pyrotechnics, and also eliminates the sealing problems associated with hydraulics.
As described in detail in the ""312 patent, the ejection system includes an on-board source of pressurized non-pyrotechnic gas, at least one release mechanism for mounting the store on the aircraft, and an actuation system for driving the release mechanism between closed and open positions. The actuation system includes an accumulator for receiving and storing pressurized gas from a source which may or may not be located on-board the aircraft. Actuation of a control valve causes a primary valve to move in a linear direction from a closed position to an open position (see FIG. 3 of the ""312 patent). This movement allows pressurized gas, i.e. air, to flow from the accumulator into the actuation chamber, forcing a separate, hook release piston to move in a linear direction as shown in the same FIG. 3 of the ""312 patent. As a result, the pressurized gas forces a ram attached to the hook release piston to engage and unlock the hooks holding the stores to the rack. Pressurized gas entering the actuator chamber is further capable of exiting from an opposite end of the actuator chamber and flowing into one or more feed tubes that deliver the pressurized gas into engagement with thrust pistons, wherein the pressurized gas causes the thrust pistons to forcibly eject the newly unlocked stores from the rack.
While the ejection system disclosed in the ""312 patent provides a significant improvement over earlier pyrotechnic ejection systems due to a substantial reduction in the amount of required maintenance that needs to be performed as compared to the maintenance performed on a pyrotechnic driven ejection system, it has been discovered that by employing a pneumatically powered primary valve reciprocating along a first axis and a separate release piston reciprocating along a second, non-aligned axis as disclosed in the ""312 patent, there is a significant reduction in the usable volume of the accumulator. This reduction in volume occurs due to the fact that the primary valve extends into a portion of the volume that would otherwise be available to the accumulator. In order for the accumulator to accommodate enough pressurized gas to provide sufficient force to unlock the hooks and forcibly eject the stores, the volume of the accumulator needs to be increased. This is achieved by increasing the outer surface area of the accumulator, as shown by the shape of accumulator 22 surrounding the actuator assembly in FIG. 2 of the ""312 patent, making it difficult for the pneumatic ejection system described in the ""312 patent to occupy the same breech volume as occupied by a conventional pyrotechnic cartridge ejection system. In effect, the ejection system disclosed in the ""312 patent is able to reduce the overall maintenance requirements of the actuator assembly at the unsatisfactory cost of an increase in size of the accumulator. As a result, the ejection system may not fit in a rack previously designed to employ a pyrotechnic cartridge without significant redesign.
Accordingly, U.S. Pat. No. 5,857,647 (hereinafter referred to as the ""647 patent) entitled INTEGRAL ACCUMULATOR VALVE AND RAM ASSEMBLY FOR PNEUMATIC WEAPON EJECTION SYSTEM, issued Jan. 12, 1999, which is herein incorporated by reference, discloses an improved ejection system comprising a pneumatic actuation assembly having a primary valve and a release ram attached thereto for reciprocating movement along a common longitudinal axis between open and closed positions in fluid communication with an accumulator which acts as a source of pressurized gas. A solenoid control valve initiates movement of the primary valve by creating a pressure imbalance across the primary valve member, allowing the primary valve member to move the attached release ram into engagement with a release mechanism capable of releasing the stores from the aircraft.
While the ""647 patent provides a significant advancement in aircraft stores ejection systems, several problems remain unaddressed. In particular, the integral primary valve and ram assembly of the ""647 patent requires the release ram to be manually reset by ground personnel after an operation cycle such that the primary valve is returned to the closed position prior to the next operation cycle. If the primary valve is not manually repositioned to the closed position, a pressure imbalance will occur during the next operation cycle, and the accumulator will not recharge with pressurized gas. The time required to reset the valve increases work load and maintenance time, as well as introducing the possibility of human error.
Another problem with conventional stores ejection systems is in the sequencing of the release ram and the release of the pressurized gas from the accumulator. More specifically, a typical problem with conventional systems, particularly with pyrotechnic racks, is that when the pyrotechnic cartridges are ignited, the cartridges not only pressurize the release mechanism, but simultaneously pressurize ejection devices that push the store away from the aircraft. As a result of this simultaneous activity, the loads experienced by the hooks securing the store are increased, which can cause the hooks to jam and not release the store. This xe2x80x9chung storexe2x80x9d condition is the result of excessive loads being introduced on the hooks during firing, effectively stalling the hook opening mechanism.
Based on the above and foregoing, it can be appreciated that there presently exists a need in the art for an ejection system actuator mechanism that utilizes pneumatic pressure to release and forcibly eject stores from their respective racks while still fitting within a conventional breech volume initially designed for pyrotechnic cartridges. There also exists a need for automatically resetting the primary valve to the closed position after an operation cycle, preferably while the aircraft is still in flight. Furthermore, there also exists a need for sequencing the movement of the release ram and the release of the pressurized air from the accumulator to the ejection devices to prevent xe2x80x9chung stores.xe2x80x9d
The present invention provides an improved stores release and ejection actuation assembly and associated method which automatically resets at the end of a release and ejection event. Advantageously, the actuation assembly of the present invention includes a bias member which automatically resets the assembly, thus eliminating the need for manually resetting the assembly as required in conventional assemblies. In addition, the actuation assembly of the present invention provides an efficient design that requires no precision adjustments.
In particular, the actuation assembly of the present invention comprises a primary valve for reciprocating movement within a fluid chamber between open and closed positions. The fluid chamber has a first portion that is in fluid communication with a pressurized gas, and a second portion that is selectively in fluid communication with either the pressurized gas or with an environment having a pressure lower than the pressurized gas. In one embodiment, an accumulator is provided for receiving and storing the pressurized gas.
The actuation assembly also preferably includes a control valve, such as a solenoid control valve, for initiating movement of the primary valve between the closed position and the open position. The control valve includes an inner valve member enclosed by a sleeve member. The inner valve member defines a passageway therethrough that cooperates with openings defined by the sleeve member for allowing fluid communication between the second portion of the fluid chamber and either the first portion of the fluid chamber or the environment having a pressure lower than the pressurized gas.
The actuation assembly of the present invention also includes a release ram responsive to the primary valve. The release ram is typically positioned outside the fluid chamber and operably connected to a release mechanism for releasing a store, such that the store is released by the release mechanism when the release ram is extended and engages the release mechanism. In one embodiment, the release ram is connected to the primary valve by a rod extending therebetween. In this regard, the primary valve functions as a release piston controlling movement of the release ram, thereby completely eliminating the need for a separate release piston assembly.
Advantageously, the actuation assembly of the present invention also includes a mechanical bias member, such as a spring, for automatically repositioning the primary valve from the open position to the closed position. In one embodiment, the bias member is disposed around the rod extending between the primary valve and the release ram and is coaxial therewith along a single longitudinal axis. The bias member is adapted for automatically resetting the primary valve after the release mechanism is fully engaged by the release ram. In one embodiment, the bias member has a constant spring rate, and may further be adapted for moving the primary valve into the closed position when no more than a predetermined pressure differential is established between the first and second portions of the fluid chamber.
According to one advantageous embodiment of the actuation assembly of the present invention, the primary valve includes a first side being selectively in fluid communication with the first portion of the fluid chamber, and a second side in fluid communication with the second portion of the fluid chamber. The first side has a surface area greater than the surface area of the second side. Advantageously, the first side has a shape selected to prevent fluid communication between the fluid chamber and a mechanism capable of forcibly ejecting the store from the aircraft, such as ejector pistons, until the release ram fully engages the release mechanism. In one embodiment, the shape of the first side of the primary valve is defined by a tab member capable of slidably engaging an opening defined by the fluid chamber that otherwise allows fluid communication between the fluid channel and the ejector pistons. In this regard, the primary valve acts to prevent the fluid chamber from being in fluid communication with the ejector pistons during movement of the release ram. Thus, it is possible to sequence the release and ejecting events such that the release ram is allowed to fully engage the release mechanism prior to the movement of the primary valve causing the tab member to be removed from the opening defined by the fluid chamber such that the fluid chamber is placed in fluid communication with the ejector pistons. As such, the release mechanism is prevented from experiencing simultaneous loads from the release ram and the ejector pistons, which can cause the hung store condition described above.
When it is desired for the primary valve to be in its closed position, the control valve is set to provide direct fluid communication between the second portion of the fluid chamber and the pressurized gas stored in the accumulator while preventing the pressurized gas from flowing from the accumulator through the control valve to the environment having a pressure lower than the pressurized gas. Pressurized gas acts against the second side of the primary valve, forcing the primary valve into contact with a valve seat.
When it is desired to open the primary valve, a signal is sent to move the control valve to an energized position, establishing direct fluid communication between the second portion of the fluid chamber and the environment having a pressure lower than the pressurized gas, such as the atmosphere. As pressurized gas in the fluid chamber vents to the atmosphere, a pressure differential or imbalance is created in the fluid chamber across the primary valve, causing the primary valve to move towards the second portion of the fluid chamber. The pressure differential causes the primary valve to unseat from the valve seat, which allows the pressurized gas occupying the first portion of the fluid chamber to flow through the opening defined by the fluid chamber that was previously plugged by the tab member and into a feed tube leading to the ejector pistons. As the primary valve continues to move towards the second portion of the fluid chamber, additional pressurized gas is able to enter the fluid chamber from the accumulator to increase the speed at which the primary valve moves toward the second portion of the fluid chamber. Because the release ram is attached for joint movement with the primary valve, the release ram rapidly moves into engagement with and unlocks the release mechanism, such as hooks, holding the stores to a rack.
During the ejection event, the control valve may be signaled to return to an unenergized position. However, the first side of the primary valve has a greater surface area than the surface area of the second side, as mentioned above. Thus, when the primary valve is in the open position, the release ram will remain in an engaged position if the pressure on the opposite sides of the primary valve is equal or even if the pressure on the second side of the primary valve is slightly greater than the pressure on the first side, if not for the bias member provided by the actuation assembly of the present invention. However, the bias member provides sufficient force to overcome the force imbalance resulting from the pressure differential across the primary valve. According to the present invention, the bias member is capable of automatically returning the release ram to a disengaged position and returning the primary valve to the closed position when the control valve is returned to the unenergized position. Advantageously, the actuation assembly of the present invention requires only a short electrical signal to energize the control valve, such as a burst, rather than requiring a constant electrical signal to the control valve.
Thus, the actuation assembly and associated method of the present invention provide an improved actuation assembly for use with an aircraft store release and ejection system. In particular, the actuation assembly of the present invention provides a bias member for automatically resetting the primary valve to a closed position, which eliminates maintenance time by ground personnel for each release cycle and eliminates human error in resetting the assembly. In one advantageous embodiment, the primary valve of the actuation assembly has a shape selected for preventing fluid communication between the fluid chamber and the mechanism capable of forcibly ejecting the stores from the aircraft until the release ram has fully engaged the release mechanism. Thus, the release event and the ejection event can be sequenced such that the release event occurs a predetermined time interval before the ejection event in order to prevent a hung store condition.